Andrusovia antecessor, Anistratenko & Neubauer & Anistratenko & Kijashko & Wesselingh, 2021

Anistratenko, Vitaliy V., Neubauer, Thomas A., Anistratenko, Olga Yu., Kijashko, Pavel V. & Wesselingh, Frank P., 2021, A revision of the Pontocaspian gastropods of the subfamily Caspiinae (Caenogastropoda: Hydrobiidae), Zootaxa 4933 (2), pp. 151-197 : 162-163

† Andrusovia antecessor sp. nov.

Fig. 4

urn:lsid:zoobank.org:act:528249A2-5494-4E14-BA1F-4AB37949EA0D

Andrusovia brusinai Starobogatov, 2000 — Neubauer et al. 2018: 54–56, fig. 6F–K, M, N [non Starobogatov, 2000].

Type material. Holotype: RGM 1309839 : 1.81 x 1.80 mm (shell height x width; Fig. 4b, c, h ) . Paratypes: RGM 1309840 : 1.52 x 1.44 mm ( Fig. 4a, d, g ) ; LV 201509 ( MSU): 1.54 x 1.55 mm ( Fig. 4e, f, i ) .

Type locality. Selitrennoye , Astrakhan region, Russia ( Table 1 , locality 1); northern Caspian Basin; GPS coordinates: 47°10’21.19”N, 47°26’25.41”E ( WGS84 ) .

Age. Hyrcanian, early Late Pleistocene, c. 107 ± 7 ka ( van de Velde et al. 2020).

Other material. 36 specimens ( RGM 1310206 ) .

Etymology. Referring to the supposed position as predecessor to modern Andrusovia . The name is a noun in apposition.

Diagnosis. Low trochiform, conical, comparably large Andrusovia with up to four well rounded whorls, wide umbilicus, broadly ovoid aperture, weakly sinuate and weakly thickened peristome.

Description (emended from Neubauer et al. 2018). Shell broad trochiform, about as high as wide, with up to 4 whorls. Rarely, specimens with slightly elevated spire occur. Protoconch high domical, about semi-circular in profile; initial part immersed; consists of 1.1 whorls, measuring 300 μm in diameter; nucleus about 90 μm wide; protoconch surface finely but strongly malleate near lower suture, rest appears eroded; P/T boundary sharp, marked by massive growth constrictions near lower suture. Teleoconch whorls highly convex, with maximum convexity in adapical half, producing slightly stepped spire. Last whorl attains 74–81% of shell height. Aperture broadly ovoid, slightly inclined, with faint concavity at contact to penultimate whorl. Peristome slightly thickened and expanded at columella and base; sinuate in lateral view, with weakly protruding central part and weak adapical indentation. Umbilicus wide, deep. Fine prosocyrt growth lines cover shell. On one specimen, traces of spiral threads occur on base.

Remarks. Neubauer et al. (2018) wrongfully attributed this species to the extant Andrusovia brusinai , which is here considered a junior synonym of Andrusovia dybowskii (see above). Andrusovia antecessor sp. nov. differs from that species in the larger size, the more whorls while having an equally small (compared to subfossil shells) or smaller (relative to recent shells) protoconch, the more regular coiling resulting in a perfectly conical shape, and the rounded whorls. The overall similarity (and the lack of other known species) suggests that both species are closely related; given the age, A. antecessor sp. nov. might be a phylogenetic predecessor of A. dybowskii .

The smaller protoconch (and thus smaller hatching size) combined with a larger adult size of Andrusovia antecessor sp. nov. compared to modern A. dybowskii suggests a faster growth rate or, alternatively, a longer lifetime. Growth rates in gastropods typically correlate positively with temperature (e.g. Kevrekidis & Wilke 2005; Shanahan et al. 2005; McCreesh et al. 2014). Similarly, the time of hatching can occur earlier under warmer conditions ( Cancino et al. 2003). The scenario of an increased growth rate in A. antecessor sp. nov. as a function of temperature fits well to the supposed warmer climate during the Hyrcanian ( Yanina 2014; Krijgsman et al. 2019).

Distribution. Endemic to the Caspian Sea, known only from the Late Pleistocene strata of the type locality. Reconstructions of the paleoecology suggest a shallow (15–25 m), lower mesohaline (5–8 psu) open lake environment ( van de Velde et al. 2020).

Figures

FIGURE 4. Andrusovia antecessor sp. nov. from the early Late Pleistocene of Selitrennoye, Astrakhan region, Russia (locality 1). (a, d, g) Paratype (RGM 1309840). (b, c, h) Holotype (RGM 1309839). (e, f, i) Paratype (LV 201509). Scale bars = 500 μm (a–f), 100 μm (g–i).